Owners and operators of containerships strive in optimizing every aspect of transport of containers while minimizing costs and environmental impacts.
One relative new proposal for optimization is to reduce the service speed of large containerships significantly whereby fuel consumption is reduced likewise significantly. In order to make up for some of the time lost during sailing, owners and operators now urge container handling facilities, or container terminals, to operate even faster.
The container handling capacity, or the performance, of container terminals using ship to shore cranes are limited by the fact that the ship to shore cranes can, due to their width, work at alternate bays of a container ship only, i.e. every second hatch of the ship is left idle without a crane.
The minimum centre distance between two of today's ship to shore cranes is about 27 m. As the centre distance between container holds of modern container ship is in the range of 15 meters only, leaving every second hatch of the ship idle, or unserviced, while loading or unloading containers, is generally accepted for the reason that this drawback simply cannot be overcome by means of today's cranes.
EP 0318264 A discloses a travelling container crane including a mobile gantry configured for sideways movement on fixed ground rails. The crane includes two parallel spaced-apart beams supported by, and extending horizontally from, the gantry in a direction perpendicular to the direction of motion of the gantry. A mobile trolley is supported under each beam and on rails fixed to the beam for to-and-from movement of the trolley along the beam. Hoist able container lifting means is suspended from each trolley. In a preferred embodiment, the third mobile trolley and the associated container-lifting device is supported between the two beams on further rails fixed to the two beams. By this, the third trolley may move along the space between the beams on the said further rails. Summarizing, the crane according to EP 0318264 A discloses a crane with a very wide portal allowing for two or more trolleys operating within the portal.
WO2008/058763 A1 discloses a high performance crane for transferring cargo to and from a ship. The crane include a boom and a trolley where the boom extends essentially perpendicular to a longitudinal rail arranged on the quay such that one end of the boom extends over the ship. The trolley is displaceably connected to a transverse rail of the boom and the trolley includes a lifting device for lifting a load or a group of loads.